Gas turbine engines generally include a high pressure compressor for compressing air flowing through the engine, a combustor in which fuel is mixed with the compressed air and ignited to form a high energy gas stream, and a high pressure turbine. The high pressure compressor, combustor and high pressure turbine sometimes are collectively referred to as the core engine. Such gas turbine engines also may include a low pressure compressor, or booster compressor, for supplying compressed air, for further compression, to the high pressure compressor.
The booster compressor typically is driven by gas turbine stages located axially aft of the higher pressure turbine stages. This configuration is common for land and marine gas turbines as well as aircraft jet engines. In one specific engine, the low pressure compressor is driven by a power turbine which also drives a load device.
With such gas turbine configurations, the low pressure spool, i.e., the low pressure compressor and the low pressure turbine, speed is set by operating conditions and is not separately variable. As a result, compressor bleed at the low pressure compressor discharge area is required for startup and transients, and for dry low emissions combustor operation at some conditions.
It would be desirable to provide a gas turbine engine wherein the low pressure compressor is operable at variable speed and flow independent of the core engine speed. Such a configuration would enable independent regulation of low pressure compressor airflow which, in turn, aids in matching low pressure compressor and high pressure compressor flow characteristics for startup, transient, and for dry low emissions combustor requirements as power is reduced.